1. Field of the Invention
This invention relates to an illumination system that splits light from a light source into a plurality of light beams, converts the light beams to one type of polarized light in which the polarization is substantially in one direction, and superposes these beams of light on the same illumination region. The invention also relates to a projector that by using the illumination system is able to display images with uniform brightness.
2. Description of the Related Art
In a projection display system apparatus, light projected onto electro-optical devices called light valves is modulated in accordance with image information and the light thus modulated is projected onto a screen to thereby display images. Liquid crystal panels (liquid crystal light valves) are the electro-optical devices usually employed. It is desirable that images displayed by a projection display system be uniform and bright, and that the light emitted by the illumination system employed in the apparatus have a high utilization efficiency. Conventionally, integrator optical systems are used to ensure uniform illumination of a region by liquid crystal light valves. Also, in projectors employing liquid crystal light valves that use modulation of just one type of linearly polarized light, in order to raise the light utilization efficiency, a polarization conversion system is used to convert unpolarized light from the light source to one type of linearly polarized light.
FIG. 24 shows the configuration of a conventional illumination system. This illumination system comprises a light source 4120, a first lens array 4130, a second lens array 4140, a polarization conversion system 4150 and a superposition lens 4160. The two lens arrays 4130 and 4140 and the superposition lens 4160 constitute an integrator optical system.
The first lens array 4130 has a plurality of small lenses 4132. The second lens array 4140 has a plurality of small lenses 4142 corresponding to the plurality of small lenses 4132 of the first lens array 4130.
The polarization conversion system 4150 has a plurality of pairs of the polarization splitting film 4152 and reflecting film 4154 arrayed in parallel along the x axis. The polarization splitting film 4152 and reflecting film 4154 have a fixed slant in the direction of the x axis that inclines counterclockwise when viewed from the z axis. The exit side of each polarization splitting film 4152 is provided with a xcex/2 retardation film 4156.
Substantially parallel light emitted by the light source 4120 is divided into a plurality of partial light beams by the plurality of small lenses 4132. The condensing action of the small lenses 4132 and 4142 converges each of the partial light beams in the vicinity of the polarization splitting film 4152 of the polarization conversion system 4150. The polarization splitting film 4152 transmits virtually all of one linearly polarized light component, such as p polarized light, for example, while reflecting virtually all of the other linearly polarized light components, such as s polarized light, for example. The linearly polarized light component reflected by the polarization splitting film 4152 is reflected by the reflecting film 4154 onto the superposition lens 4160. The linearly polarized light component transmitted by the polarization splitting film 4152 falls incident on the xcex/2 retardation film 4156, is converted to linearly polarized light having the same polarization direction as the other linearly polarized light component, and falls incident on the superposition lens 4160. Thus, the multiple partial light beams incident on the superposition lens 4160 are converted into substantially one type of linearly polarized light and substantially superposed at the illumination region 4180. This enables the illumination region 4180 to be illuminated substantially uniformly by substantially one type of linearly polarized light.
In the above conventional illumination system, the partial light beams formed by the first lens array 4130 are converged in the vicinity of the polarization splitting film 4152, and as a result, the partial light beams that fall incident on the polarization splitting film 4152 are spatially separated. The reflecting film 4154 is positioned where there are no partial light beams, and reflects linearly polarized light reflected by the polarization splitting film 4152. In this way, unpolarized light emitted by the light source is separated into two types of linearly polarized light by the polarization splitting film 4152 and the reflecting film 4154.
If the light source 4120 emits a perfectly parallel beam, the partial light beams will be converged to substantially a point in the vicinity of the polarization splitting film 4152. However, if in practice the beam from the light source 4120 is not perfectly parallel, the image will be formed with some degree of divergence. The width of the polarization splitting film 4152 and reflecting film 4154 along the x axis is set so that almost all of the light used to form the image falls effectively on the polarization splitting film 4152.
An effective way of obtaining a brighter image with a projector is to increase the output of the light source lamp. Light source lamps that are used include metal halide lamps and mercury lamps. To increase the light output it is preferable to use a lamp having a long arc. Usually, however, the beam emitted by a long-arc lamp is less parallel than a beam emitted by a short-arc lamp. This means that even if a short-arc lamp used in an illumination system is simply replaced by a long-arc lamp, the decreased parallelism of the beam will result in a lower proportion of the light impinging on the polarization splitting film 4152, reducing the polarization splitting efficiency. Thus, the problem is that even when the light source output is increased, there is not much of an increase in the effective output of the light used to illuminate the illumination region.
An object of the present invention is to provide a technology that, in an illumination system that includes an integrator optical system and polarization conversion system that uses a light source lamp with a higher output than a conventional lamp, allows the light output to be increased without decreasing the utilization efficiency of the illumination system. Another object is to provide a projector that enables a brighter, more uniform projection image to be obtained.
At least part of the above and the other related object are attained by an illumination system that illuminates a light incident surface of an optical device as an illumination region. The system comprises: a light source that emits unpolarized light, a power variation optical relay system that changes a size of a light beam emitted by the light source, a superposition optical system that effects illumination of the illumination region by a given incident light beam, and a polarization conversion system that is provided at a selected position along a light path from an incident surface of the power variation optical relay system to an exit surface of the superposition optical system to convert an incident beam of unpolarized light to a light beam having a linearly polarized component with one type of polarization direction and emits the converted light beam. A size of a light beam entering the polarization conversion system is reduced in a prescribed direction by the power variation optical relay system.
In the illumination system of the present invention the size of a beam of light entering the polarization conversion system can be reduced in a prescribed direction by a power variation optical relay system, thereby improving the incident efficiency of light entering the polarization conversion system. As a result, the illumination region can be brightly and uniformly illuminated by one type of linearly polarized light with substantially uniform directions of polarization. In general, since there is a proportional relationship between the output of a light source lamp and arc length, and the parallelism of the light beam emitted by the light source lamp deteriorates as the arc length increases, when a high output lamp is used there is a decrease in the light incident efficiency with respect to the polarization conversion system. However, in accordance with the configuration of this invention, when a light source lamp having a higher output than a conventional lamp is used, it is possible to increase the brightness of the illuminating light comprised of light polarized in the same direction without decreasing the utilization efficiency of the illumination system. Here, the prescribed direction, with respect to the light beam, means one or two directions orthogonal to the direction of light beam propagation. Therefore when the power variation optical relay system is constituted using an optical condensing element having a uniform power in every direction such as a spherical lens, the size of the beam section is decreased in every direction correspondingly. Also, when the power variation optical relay system is constituted using an optical condensing element having a power in only one direction such as a cylindrical lens, the size of the beam section is decreased in the one direction only.
In accordance with one preferable structure of the optical illumination, the power variation optical relay system includes: a first lens array having a plurality of first small lenses, a relay lens array having a plurality of relay lenses that is disposed on a light emission side of the first lens array, and a second lens array having a plurality of second small lenses that is disposed on a light emission side of the relay lens array. The first lens array and the second lens array are disposed at conjugate points of the relay lens array. The polarization conversion system includes: a polarization beam splitter array that has a plurality of pairs of mutually parallel polarization splitting film and reflecting film in an inclined state along the prescribed direction and separates the incident beam of unpolarized light into a plurality of partial light beams each having two types of linearly polarized light, and a polarization conversion device that converts a polarization direction of a first type of linearly polarized light of the two types of linearly polarized light to a same polarization direction as a second type of linearly polarized light. A light beam entering the polarization conversion device is split by the power variation optical relay system into a plurality of partial light beams, and the size of each of the plurality of partial light beams in the prescribed direction is reduced by the power variation optical relay system.
In this arrangement the power variation optical relay system is constituted by an array of lenses, thereby enabling the incident light efficiency in respect of the polarization conversion system to be improved. If the focus is on improving the incident light efficiency with respect to the polarization beam splitter array, a power variation optical relay system can be employed that uses an optical condensing element curved in one direction such as the cylindrical lens described above.
In this configuration, it is preferable that the superposition optical system includes: a third lens array having a plurality of third small lenses on which the plurality of partial light beams entering the superposition optical system impinge, a fourth lens array having a plurality of fourth small lenses corresponding to the plurality of third small lenses, and a superposition lens that superposes onto the illumination region a plurality of partial light beams passing through the third lens array and the fourth lens array.
Using a superposition optical system configured as described allows virtually all of the light exiting from the polarization conversion system to be guided to the illumination region, thereby improving the light utilization efficiency of the illumination system and enabling the illumination region to be illuminated more uniformly.
The superposition optical system may includes: a third lens array having a plurality of small lenses that superposes the plurality of partial light beams substantially on the illumination region, and a fourth lens array having a plurality of fourth small lenses corresponding to the plurality of third small lenses.
In this case, the angle of incidence of the illuminating beam incident to the illumination region can be made smaller compared to that in a superposition optical system comprised of third and fourth lens arrays and superposition lens. When optical systems and elements in which the optical characteristics depend on the angle of incidence are located in the illumination region, this allows the light utilization efficiency of such systems and elements to be improved. It also serves to reduce the complexity and cost of the illumination system.
In accordance with the above configurations, it is preferable that the polarization conversion system is disposed between the power variation optical relay system and the superposition optical system. The polarization conversion system may be disposed between the relay lens array and the second lens array of the power variation optical relay system. The polarization conversion system may be disposed between the third lens array and the fourth lens array.
Whichever location is used for the polarization conversion system, it is possible to improve the efficiency of light entering the polarization conversion system, as described above. However, the improvement is greater when the polarization conversion system is located between the relay lens array and the second lens array or between the third and fourth lens arrays, than when it is located between the power variation optical relay system and the superposition optical system.
Moreover, when the polarization-conversion system is located between the power variation optical relay system and the second lens array or between the relay lens array and the second lens array of the power variation optical relay system, the second and third lens arrays may be optically integrated.
xe2x80x9cOptically integratedxe2x80x9d elements mean a combination of optical elements bonded together with adhesive, or a single optical element possessing the functions of multiple optical elements. The functions of the second lens array of the power variation optical relay system and the functions of the third lens array of the superposition optical system may be integrated into either one of the lens array while omitting the remaining lens array. Optically integrating multiple optical elements (the second and third lens arrays) enables optical loss arising at interfaces between the elements to be reduced, thereby improving the light utilization efficiency. It also enables the complexity and cost of the optical system to be reduced.
In accordance with the above configuration, it is preferable that the plurality of first small lenses of the first lens array each has a different optical axis position in a direction perpendicular to the prescribed direction so that a plurality of partial light beams entering the polarization conversion system are mutually adjacent in at least the direction perpendicular to the prescribed direction. xe2x80x9cPrescribed directionxe2x80x9d means the direction in which, in the polarization conversion system, the multiple sets of alternating polarization splitting film and reflecting film are arranged.
By thus enabling the angle of incidence of the illuminating beam incident to the illumination region to be reduced, when the optical systems and elements are located in the illumination region this allows the light utilization efficiency of such systems and elements to be further improved. It also enables the optical system along the light path from the polarization conversion system to the illumination region to be reduced in size.
In this configuration, a plurality of partial light beams arrayed in the prescribed direction may be each reduced in the power variation optical relay system by a reduction ratio that differs according to an array position of each partial light beam.
This makes it possible to further reduce the angle of incidence of the illuminating beam incident to the illumination region, and, as such, when optical systems and elements in which the optical characteristics depend on the angle of incidence are located in the illumination region, allows the light utilization efficiency of such systems and elements to be further improved.
In accordance with the above configurations, the relay lenses may be constituted by a composite lens comprising at least two lenses.
Constituting the relay lenses as a composite lens enables correction of chromatic aberration, spherical aberration and astigmatism and the like that readily arise in the case of a single lens configuration.
The present invention is also directed to a first projector for displaying projected images. The first projector comprises: any one of the above illumination systems, an electro-optical device that converts light received from the illumination system to light for forming images responsive to image signals and emits the light thus converted, and a projection optical system that projects light emitted from the electro-optical device.
The first projector uses the illumination system of the invention, so that even when a light source lamp is used having a higher output than a conventional lamp, the light output can be increased without decreasing the utilization efficiency of the illumination system. This allows a brighter, more uniform projection image to be obtained. As the first projector of the invention, there can be envisioned a sequential color display system apparatus with a monochrome liquid crystal panel and a time-division system in which color filters or the like able to generate specific colors are used.
The first projector further may comprise: a color separator that separates light emitted from the illumination system into a plurality of color components, a plurality of the electro-optical devices for separately receiving each of the color components separated by the color separator, and a color combiner for combining light of each color component emitted by the plurality of electro-optical devices, wherein the projection optical system projects the combined light emerging from the color combiner.
This arrangement permits brighter, more uniform color projection images to be obtained.
In this configuration, it is preferable that, assuming x, y, z as three mutually orthogonal directional axes where z is a direction parallel to an optical axis of light emerging from the illumination system, the color separator has a color separation surface plane that is substantially perpendicular to plane xz and is inclined by a prescribed angle with respect to plane yz, and the illumination system is positioned so that the prescribed direction in which a plurality of pairs of polarization splitting film and reflecting film included in the polarization conversion system are arrayed is substantially identical to the y direction.
In accordance with this arrangement, the prescribed direction in which the multiple pairs of polarization splitting film and reflecting film are arrayed in the polarization conversion system (hereinafter referred to as the polarization splitting direction) is perpendicular to the direction of color separation in the color separation surface plane of the color separator, so the range of variation of the angle of incidence of the light incident on the color separation surface can be reduced. Since the color separation characteristics of the color separation surface depend on the angle of incidence, reducing the range of variation of the angle of incidence reduces deviation in the colors of light exiting the color separator. As a result, projection images can be obtained that have more uniform brightness and colors.
It is also preferable that, assuming x, y, z as three mutually orthogonal directional axes where z is a direction parallel to an optical axis of light emerging from the illumination system, the color combiner has a color combining surface plane that is substantially perpendicular to plane xz and forms a prescribed angle with respect to plane yz, and the illumination system is positioned so that the prescribed direction in which the plurality of pairs of polarization splitting film and reflecting film are arrayed is substantially identical to the y direction.
In accordance with this arrangement, the prescribed direction in which polarized light is separated in the polarization conversion system is perpendicular to the direction of color combining in the color combining surface plane in the color combiner, thereby enabling the range of variation of the angle of incidence of the light incident on the color combining surface to be reduced. Since the color combining characteristics of the color combining surface depend on the angle of incidence, reducing the range of variation of the angle of incidence reduces deviation in the combined colors leaving the color combining surface. As a result, projection images can be obtained that have more uniform brightness and colors.
The present invention is further directed to a second projector for displaying projected images, comprising: any one of the above illumination systems, a reflecting type electro-optical device that converts incident light to light for forming images responsive to received image signals while reflecting the light, a projection optical system that projects light emitted from the reflecting type electro-optical device, and a polarization splitting device that directs first linearly polarized light emitted from the illumination system toward the reflecting type electro-optical device and also directs toward the projection optical system second linearly polarized light that is received from the reflecting type electro-optical device and that is polarized in a direction perpendicular to the first linearly polarized light.
The second projector also uses the illumination system of the invention, so that even when a light source lamp is used having a higher output than a conventional lamp, the light output can be increased without decreasing the utilization efficiency of the illumination system. Thus, projection images can be obtained that are brighter and have more uniform brightness and colors.
In this configuration, it is preferable that, assuming x, y, z as three mutually orthogonal directional axes where z is a direction parallel to an optical axis of light emerging from the illumination system, the polarization beam splitter element has a polarized light separation surface plane that is substantially perpendicular to plane xz and is inclined by a prescribed angle with respect to plane yz, and the illumination system is positioned so that the prescribed direction in which a plurality of sets of polarization splitting film and reflecting film included in the polarization conversion system are arrayed is substantially identical to the x direction.
When linearly polarized light that within plane yz is inclined in the z direction falls on the color separation surface, the rotation of the polarization axis reduces the utilization efficiency of light utilized in a reflecting type optoelectric apparatus. Since in accordance with the above configuration the range of variation in the angle of incidence of light falling on the polarized light separation surface can be made smaller in plane yz than in plane xz, the polarization axis rotation can be reduced. This results in projection images that are brighter and have higher contrast.
The present invention is also directed to a third projector for displaying projected images, comprising: any one of the above illumination systems, an electro-optical device that includes a plurality of pixels each including a plurality of sub-pixels corresponding to light of each of a plurality of colors and a condenser optical system comprising a plurality of small condenser lenses corresponding to each pixel. The electro-optical device converts light transmitted by each pixel to light for forming image of each pixel responsive to given image information. The projector further comprises a color separator that separates light emerging from the illumination system into a plurality of colors and also directs light of each of the plurality of color components in a mutually different direction to impinge on the sub-pixels corresponding to the respective color components, and a projection optical system for projecting light emitted from the electro-optical device.
The third projector according to the invention also uses the illumination system of the invention, so that even when a light source lamp is used having a higher output than a conventional lamp, the light output can be increased without decreasing the utilization efficiency of the illumination system, thereby making it possible to obtain projection images that are brighter and have more uniform brightness and colors.
In this configuration, it is preferable that, assuming x, y, z as three mutually orthogonal directional axes where z is a direction parallel to an optical axis of light emerging from the illumination system, the color separator has a plurality of color separation surface planes for selectively separating light into a plurality of color components that is substantially perpendicular to plane xz and is inclined by a different prescribed angle with respect to plane yz, and the illumination system is positioned so that the prescribed direction in which a plurality of pairs of polarization splitting film and reflecting film included in the polarization conversion system are arrayed is substantially identical to the y direction.
In accordance with this arrangement, the direction in which polarized light is separated in the polarization conversion system is perpendicular to the direction of color separation in the color separation surface plane of the color separating optical system, thereby enabling the range of variation of the angle of incidence of the light incident on the color separation surface to be decreased. Since the color separation characteristics of the color separation surface depend on the angle of incidence, reducing the range of variation of the angle of incidence reduces deviation in the colors of light exiting the color separating optical system. As a result, projection images can be obtained that have more uniform brightness and colors.
It is also preferable that the illumination system is positioned so that the prescribed direction in which a plurality of pairs of polarization splitting film and reflecting film are arrayed is substantially identical to a direction that is perpendicular to a direction in which the plurality of sub-pixels of each pixel are aligned.
Since in accordance with this arrangement the direction in which polarized light is separated in the polarization conversion system is perpendicular to the direction in which is arrayed the plurality of color sub-pixels included in each pixel, it is possible to reduce the color shift due to the incident light that is not relevant to each color sub-pixel.
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with the accompanying drawings.